Receipt of Medications for Chronic Disease During the First 2 Years of the COVID-19 Pandemic Among Enrollees in Fee-for-Service Medicare

This cohort study examines changes in prescription fill rates of 5 groups of medications for chronic diseases during the first 2 years of the COVID-19 pandemic among enrollees in fee-for-service Medicare.


eAppendix 1. Identification of Beneficiaries Who Were Institutionalized for Study Exclusion
Nursing home residence was determined using place of service and Current Procedural Terminology codes from the Carrier (physician)and Outpatient files to identify enrollees with any nursing facility-related services in each month. If the beneficiary had 1 or more nursing facility-related place of service or Current Procedural Terminology codes in the relevant period, the beneficiary was classified as a nursing home resident.
There was an annual decline in fee-for-service populations for Black enrollees (-5.55%) and Hispanic enrollees (-2.81%) enrollees. This is likely because of the rapid increases for Hispanic and Black Medicare enrollees in Medicare Advantage (Meyers et al., 2021). When fee-forservice Medicare enrollees sign up for Medicare Advantage, enrollment begins in January, which is consistent with the sudden drop in fee-for-service enrollment in January relative to December of the previous year. There could be an additional impact of higher mortality rates for Black and Hispanic enrollees during the COVID-19 pandemic (Gilstrap et al., 2022).
The largest decline is for ADRD patients (-15.39%) but this is the consequence of the way that the cohort was constructed. Because we were concerned that during the pandemic there would have been under-diagnosis of ADRD, we deemed anyone who had been diagnosed with ADRD during 2019-2021 to have ADRD for the entire period of analysis. Thus someone who was diagnosed with ADRD in 2020, and who died in 2021, would be in the "ADRD" cohort from January 2019 through their death in 2021. Because of the high rate of mortality among ADRD patients -almost 20% in 2019, prior to the pandemic, and nearly 25% in 2020 (Gilstrap et al., 2022), this means that the sample is expected, by construction, to experience attrition during the period of analysis.
The cohort of beneficiaries with Alzheimer's Disease and Related Dementias (ADRD) was defined as those with one or more diagnosis appearing on one or more claim 2019-2021. This inclusive approach was chosen to maximize ascertainment of beneficiaries with this condition for our monthly prescription fill measures. Dependence on monthly appearance of the diagnosis on a claim for the monthly cohorts would have missed many beneficiaries diagnosed with the condition.  Gilstrap et al., 2022). We adopt the conservative approach of using as the sample size the average enrollment for the entire year despite the presence of multiple fills within each year. Variances are calculated using the exact binomial approach.

eAppendix 4. Medications Included in Each Drug Group of Interest
For the index (or average) measures across the 5 treatment groups, we account for the positive covariance of the fills by month; that is, in months where diabetes drugs rise or fall, there is empirical evidence of a greater likelihood of (e.g.) anti-depressants rising and falling as well.
(This has the effect again of making the confidence intervals wider than if the 5 fill rates were independent.) Defining z as the average across the five drug classes in a given year: A.3 The monthly data on each of the five measures during the pre-pandemic period exhibits a high degree of correlation, on the order of 0.8 to 0.9. This means that assuming that the index consists of 5 independent random variables will lead to a confidence interval that is too tight. For this reason, we assume the extreme case that each of these 5 components are perfectly correlated (e.g., the correlation coefficient is equal to one), it is straightforward to show that the variance of the index is written as: A.5 ( )